If an instrument required or permitted by law to be registered has no subscribing witness, the execution of the same may be proven before any official authorized to take the proof and acknowledgment of such instrument by proof of the handwriting of the maker and this shall likewise apply to proof of execution of instruments by married persons. (1899, c. 235, s. 11; Rev., s. 998; C.S., s. 3304; 1945, c. 73, s. 12; 1977, c. 375, s. 12.)